1. Technical Field of the Invention
The invention is in the general field of switching mechanisms, with specific applicability to rotary switching mechanisms, such as for switching optical devices.
2. Description of the Related Art
There is a continuing need for movement of devices in and out of locations, such as in swapping of optical filters or other optical elements in and out of an optical path. The simplest switch mechanisms do not contain any provision for reducing the reaction forces and moments. For systems that are not sensitive to vibrations or systems that do not require the switch to occur in a very short period of time, this simple approach may be adequate. However, as systems increase in performance they can become more susceptible to vibration.
In some prior systems, a reaction mass has been added to the switching mechanism. Instead of applying a torque between the moving element and the base, a torque is applied between the moving element and the reaction mass. The reaction mass and the moving element move in opposite directions, and theoretically no torque is applied to the base. This approach has various disadvantages, the most severe of which is that the mass is usually approximately equal in size and weight to the primary moving element. The added size, weight and complexity of the reaction mass make packaging difficult and add significant weight to the system. The power consumption of this type of mechanism will also be higher than an equivalent mechanism without a reaction mass. This approach has been used extensively on gimbals and beam steering mirrors.
In systems where there are at least two elements and one of them is always deployed and the rest are always retracted, the torque applied to the element that moves from deployed to retracted can be used to cancel torque of the element that moves from retracted to deployed. This approach is essentially the same as the reaction mass approach described above except that another mechanism which is mounted to a common base is used as the reaction mass. Instead of a torque applied directly between the primary moving element and the reaction mass (requiring one actuator), each of the two moving elements applies a torque to a common plate (requiring two actuators). Because the two mechanisms are rotating in opposite directions, it is possible to cancel the reaction torques resulting in a reactionless system.
In the systems described above, an actuator is usually the sole source of the torque that moves the masses from one position to another. The actuator typically is the dominant source of heat dissipated in the mechanism. In many systems, the mechanism needs to operate in a cryogenic environment and any heat that the mechanism adds needs to be removed in order to maintain that cryogenic environment. It will be appreciated that having heat sources in a cryogenic system is undesirable.
From the foregoing it will be appreciated that there is room for improvement in the general area of rotary switching mechanisms.